(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method for the inspection of damage that is incurred in the perimeter or edge of a wafer during and as a result of wafer processing.
(2) Description of the Prior Art
The creation of semiconductor devices uses large-diameter silicon wafers that have been created by separating or cutting these wafer from silicon ingots of cylindrical shape. For the handling of the created wafers, methods of automation are applied whereby the wafers are mounted in for instance wafer cassettes or wafer boats. Wafer cassettes and wafer boats are typically used for the transportation of wafers from one processing station to another processing station, for the storage of wafers, for storage of wafers as part of a temporary interruption of a processing sequence, for loading and positioning wafers in a processing chamber. On other occasions, wafers are positioned into a processing location by robotic controlled lifting and positioning devices or are moved through a processing station using automatic methods (such as a conveyer belt) of positioning the wafer into, within and exiting from a processing station.
Most of these operations require a physical interface between the wafer that is being transported and the transporting interface. To facilitate this physical interface, a surface area around the perimeter of the wafer is typically not used for the creation of semiconductor devices but is reserved exclusively as a means of handling the wafer.
Many of the tools and mechanisms that are used for the transportation of wafers are of a sophisticated nature and are carefully crafted with the objective of minimizing or avoiding any damage that can potentially occur in the surface (perimeter) of the wafer where the physical contact with the wafer is typically established. Despite these delicate and sophisticated methods that are used for transporting wafers, wafer damage of some sort is to be expected, which imposes the need for wafer inspection at critical points in the chain of wafer transportation.
Wafer inspection, which has as objective to detect and identify damage that is incurred by the wafer in the transportation and handling thereof, is typically performed by visually inspecting the wafer for damage. This method is however open to human error or oversight and can therefore be improved, thus eliminating unnecessary wafer loss or oversight of existing wafer damage.
The invention provides such a method of inspecting wafers by eliminating visual, operator performed inspection of wafers. By applying an ultrasound-based methodology, the inspecting of wafers can be significantly improved with regard to accuracy and speed and throughput of inspection.
U.S. Pat. No. 5,955,673 (Leroy et al.) shows an ultra sound inspection method for a cathode target.
U.S. Pat. No. 6,188,050 (Duffer et al.) describes a laser ultrasonic application as a way to measure wafer temperature.
U.S. Pat. No. 6,045,434 (Fisher, Jr. et al.) shows an ultrasound method to monitor CMP pad life.
U.S. Pat. No. 5,797,845 (Barabash et al.) shows an ultrasound imaging technique.